A main goal of the proposed CCNE is to develop nanosystems that specifically seek out tumor tissue for the purposes of diagnosing, monitoring and treating tumors. Each of these applications requires selective delivery of nanoparticles into tumors and/or selective detection/activity in tumors. Particles capable of specifically entering into parenchymal or stromal tumor cells provide further advantages. In addition, particles designed for certain in vivo diagnostic purposes should be able to exit from tumor cells they have entered, allowing for send and return type approaches. This project (Project 1) focuses on the development of homing peptide-nanoparticle constructs that optimize tumor homing while avoiding non-specific accumulation in non-target tissues and minimizing toxicity. A large collection of peptides and other compounds capable of selectively delivering nanoparticles to tumor vasculature is on hand. The biggest single obstacle to be overcome in optimizing the tumor homing of such particles is the ability of the reticuloendothelial system (RES) and macrophages to eliminate particles from the systemic circulation. The ability of the peptides to effect passage of the particles into the extravascular space, and internalization of the particles and their payload into tumor cells and tumor endothelial cells are also major determinants in targeting efficacy of nanoparticles. We propose to develop new technology to deal with the liver uptake and extravasation issues, and we also propose to develop ways of promoting the exit of nanoparticles from cells, a trait that could be useful in some in vivo diagnostic applications, and could also reduce non-specific toxicities to non-intended target cells. A team of tumor biologists, peptide chemists, materials scientists, and engineers endeavor to achieve these goals by identifying and characterizing peptides from combinatorial libraries that promote the binding and intracellular entry in tumors and discourage it elsewhere in the body. We expect this work in Project 1 to provide the basis for rational design of nanoparticle systems with greatly improved in vivo properties for effective tumor targeting due to diminished liver uptake and ability to travel through barriers such as cell layers and membranes. The results from this Project will enable the design of in vivo routing systems for multifunctional nanodevices. The proposed use of in vivo discovery methods and early in vivo testing and optimization of the routing systems will accelerate the construction of devices that are likely to be clinically useful. These peptides, and the existing collection of homing peptides that recognize specific receptors in tumor vessels and/or on tumor cells, will be available to the other Projects in this CCNE. The validity of the peptides as nanoparticle delivery vehicles and applicability of the results to human cells and tissues will be validated in conjunction with Projects 2 and 6 of this CCNE.